Chewing gum manufacturers have long endeavored to provide longer lasting flavors in chewing gums. In one approach to prolonging flavor, ingredients including flavors, sweeteners, and food-grade acids (to provide sourness) have been encapsulated with polymers to delay and prolong their release. See, for example, U.S. Pat. Nos. 4,931,293, 5,057,328, 5,064,658, and 5,110,608 to Cherukuri et al. In another approach, a flavor is extended by providing a chewing gum composition that includes a gum base, at least one flavor, and at least one encapsulated surfactant, where the surfactant increases the amount of flavor released from the chewing gum composition. See, for example, U.S. Patent Application Publication No. US 2006/0263474 A1 of Luo. However, delaying the release of food-grade acids has been particularly difficult, perhaps because of their extremely high water solubility. It has therefore been difficult to provide a long-lasting sour flavor. Moreover, with the current interest in flavor-changing chewing gums, it has not been possible to prepare an acceptable flavor-changing gum that features a sour flavor as the second or subsequent flavor of the gum. There is therefore a need for materials and methods capable of delaying and extending the release of food-grade acids in chewing gum.